Computational challenges in the characterization of magnetism for atomically precise nanographenes on noble metal substrates.

On-surface synthesis techniques have demonstrated high flexibility and atomic precision in the fabrication of carbon-based nanomaterials, with recent examples ranging from graphene nanoribbons hosting topological quantum phases¹ to specifically shaped nanographenes (NGs).^2-5 NGs may exhibit a magnetic, open-shell structure as a result of their peculiar topology, which makes them highly attractive for applications in molecular electronics. Furthermore, unpaired spins in open-shell NGs may be used to perform spin logic operations.
I will discuss present challenges for ab-initio simulations in understanding recent experiments reporting
evidence of magnetism for specific nanographenes supported on gold substrates. I will present both, cases of
non-Kekulé NGs where sublattice imbalance is responsible for magnetism, and of NGs where - despite absence
of sublattice imbalance - topological frustration in the underlying π-electron network generates uncompensated
radicals.

¹O. Groening et al. Nature 560, 209–213 (2018)
²S. Mishra et al. Nature Commun. 9, 1714 (2018)
³S. Mishra et al. ACS Nano, 12, 11917 (2018)
⁴S. Mishra et al. J. Am. Chem. Soc. 141, 10621 (2019).
⁵J. Liu et al. J. Am. Chem. Soc. 141, 12011 (2019).